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CHM 11500 Lecture 29: Material Chemistry

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School
Purdue University
Department
Chemistry
Course
CHM 11500
Professor
Chittaranjan Das

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CHM 11500 Full Course Notes
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CHM 11500 Full Course Notes
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Document Summary

Chm 115 - lecture 29 - material chemistry. In a collection of atoms, there is a finite number of discrete energy levels available for the electrons of those atoms. As the number of atoms in the group increases so does the number of available energy levels. As the number of available energy levels increases, the different available levels become closer and closer in energy, and form a seemingly continuous band of available energy levels. Electrons will fill the band of energy levels from the bottom up. Because of the way electrons fill the band, there will be a filled band at the bottom, known as the valence band. The unfilled band at the top is known as the conduction band. The band gap in between them is the energy difference between them. The size of the band gap is what determines the electrical properties of the material: Band gap energy is known as eg.

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Related Questions

The conduction of electricity inmaterials is explained in terms of band theory. The band that isformed from the filled bonding molecular orbitals is called thevalence band, and the band that is formed from the emptyantibonding molecular orbitals is called the conductionband. The energy difference between these bands is known as theband gap energy, or the band gap.

Click on the image below to explore the activity, which will help you to identify the insulator and thetypes of semiconductors based on band gap energy. Blue-coloredbands indicate conduction bands, and red-colored bands indicatevalence bands.

When you click on each box, you will observe the changes in bandgap energy for that material.
Part A
In the interactive activity, the bandshown at the top is the conduction band, and the band shown at thebottom is the valence band. The valence band consists of bondingmolecular orbitals that are filled with electrons, and theconduction band consists of vacant antibonding molecular orbitals.The red color indicates that the orbitals in that band are filledwith electrons, and the blue color indicates that the orbitals inthat band are empty. The space between the two bands shows theenergy difference between them and is known as the band gapenergy, or the band gap.

Which of the following statements are correct with respect tothe band structure and the band gap of different materials?

Check all that apply.
Check all that apply.
SubmitHintsMy AnswersGive UpReviewPart
Part B
When you add a controlled amount ofsubstance known as an impurity to a pure semiconductor, itsconductivity increases. This process is known as doping. Theaddition of an impurity can increase or decrease the number ofavailable electrons. If the number of electrons is increased, theextra electrons conduct electricity. If the number of electrons isdecreased, a vacant hole is created. The adjacent electron entersthe vacant hole and conducts electricity. Thus, it seems like theholes act as charge carriers. They are considered to be positivecharge carriers. Depending upon the charge carriers that conductelectricity, there are two types of semiconductors: p-typesemiconductors and n-type semiconductors.

Which of the following statements are correct with respect tosemiconductors?

Check all that apply.
Check all that apply.
The undoped semiconductor has a partiallyfilled conduction band.
The n-type semiconductor has apartially filled valence band.
The p-type semiconductor has apartially empty conduction band.
The p-type semiconductor has apartially empty valence band.
The band gap of a semiconductor is lessthan that of an insulator.
The conduction band for insulators isalways vacant.
SubmitHintsMy AnswersGive UpReviewPart
Part C
Germanium is a group 4A semiconductor. Theaddition of a dopant atom (group 3A element) that has fewer valenceelectrons than the host atom results in a p-typesemiconductor. The addition of a dopant atom (group 5A elements)that has more valence electrons than the host atom results in ann-type semiconductor.

Which of the following elements when used for doping germaniumwill yield p-type semiconductors, and which elements whenused for doping germanium will yield n-typesemiconductors?

Drag the appropriate elements totheir respective bins.
The conductivity of semiconductors can beincreased by the doping process.
The addition of group 3A elements to group4A semiconductors decreases the conductivity of the group 4Asemiconductors.
As the temperature increases, theconductivity of semiconductors decreases.
Holes are charge carriers in p-typesemiconductors.
The addition of group 5A elements to group4A semiconductors increases the conductivity of the group 4Asemiconductors.
Electrons are charge carriers inn-type semiconductors.
SubmitHintsMy AnswersGive UpReviewPart
Part D
Observe the band structure for fourdifferent substances in the following figure. The band shown at thetop is the conduction band, and the band shown at the bottom is thevalence band. The red color indicates that the orbitals in thatband are filled with electrons, and the blue color indicates thatthe orbitals in that band are empty. Identify which band structurecorresponds to which substance.
Drag the appropriate labels totheir respective targets.

Please answer these for me im totally confused
001 10.0 points
Consider the atoms
A) nitrogen B) bismuth C) arsenic
Arrange them in order of increasing first
ionization energy.
1. A, C, B
2. B, A, C
3. C, B, A
4. B, C, A
5. A, B, C
6. C, A, B


002 10.0 points
Which of the following is a measure of the
tendency of an atom in a molecule to attract
electrons to itself ?
1. L nonbonding
2. polar
3. electronegativity
4. ionization


003 10.0 points
Which ion has the larger radius?
1. Unable to determine
2. Both have same radius.
3. Sn
2+
4. Sn
4+


004 10.0 points

Which of the following statements is true?
1. Electron affinity is a measure of the
amount of energy needed to remove an electron from an atom.
2. As electron affinity increases (becomes
increasingly negative), electronegativity decreases.
3. Electronegativity is a measure of the tendency of an atom tolose electrons.
4. When ionization energy increases, electronegativityincreases.
5. Ionic radii are always larger than atomic
radii for the same element.


005 10.0 points

Which of the following is a true statement?
1. There is no relationship between atomic
size and ionization energy.
2. Ionization energy increases as electronegativitydecreases.
3. Electronegativity increases as electron
affinity decreases (gets more positive).
4. None of these
5. Ionization energy increases as atomic size
decreases.


006 10.0 points
Which of the following correctly rationalizes
the increase in atomic radii down and to the
left on the periodic table, based on what we
discussed in class?
1. None of these. Atomic radii increase up
and to the right.
2. Because the elements are easier to ionize, they have a largerelectronegativity, and
therefore their electron affinity is not suffi-
cient to reduce atomic radii.penwell (blp865) – HW 12 PeriodicTrends – thompson – (991918292) 2
3. Larger elements have an increasing proportion of d and forbitals, which are intrinsically larger than all of the s and porbitals.
4. As you move to the left across a period,
decreasing ENC means the outer electrons
are less tightly held and can move further
from the nucleus. As you move down a group,
the electrons occupy orbitals that are further
from the nucleus.
5. The elements are simply larger due to
more protons and neutrons.
6. The periodic table was set up to group
atoms by size to facilitate comparisons.


007 10.0 points
In a series of species with the same total set
of electrons present, one observes that
1. the radii would increase as the atomic
number increases.
2. the radii would decrease as the atomic
number increases.
3. the radii would decrease as the number of
electrons increases.
4. all have the same radius.
5. the radii would increase as the number of
electrons increases.


008 10.0 points
The ions Na
+
, F
−
, and O
2−
each have ten
electrons. What would be the order of the
sizes of these three ions?
1. Na
+
is smaller than O
2−
which is smaller
than F
−
.
2. O
2−
is smaller than Na
+
which is smaller
than F
−
.
3. F
−
is smaller than O
2−
which is smaller
than Na
+
.
4. F
−
is smaller than Na
+
which is smaller
than O
2−
.
5. Na
+
is smaller than F
−
which is smaller
than O
2−
.
009 10.0 points
Which of the following atoms has the largest
radius?
1. K
2. Mg
3. Li
4. Br
5. Si
010 10.0 points
Why is it harder to remove an electron from
fluorine than from carbon, or, to put it another way, why are thevalence electrons of
fluorine more strongly bound than those of
carbon?
1. The valence electrons of both fluorine and
carbon are found at about the same distance
from their respective nuclei but the greater
positive charge of the fluorine nucleus attracts
its valence electrons more strongly.
2. Fluorine has more valence elctrons than
does carbon.
3. Carbon has a lower atomic mass than
does fluorine.
4. Fluorine has a nearly filled octet, which
is always more stable than a partially filled
octet.
5. The statement is false; it takes very nearly
the same energy to remove an electron from
(ionize) both elements.
011 10.0 points
In general, ionization energy tends to increasepenwell (blp865) –HW 12 Periodic Trends – thompson – (991918292) 3
in the periodic table
1. from bottom to top and from right to
left.
2. in no regular trend.
3. from bottom to top and from left to
right.
4. from top to bottom and from right to
left.
5. from top to bottom and from left to
right.
012 10.0 points
Consider the most stable ions which are
formed by the elements Cs, Ba, Te and I.
Which element will form the ion with the
largest radius? (Hint: the ions will be isoelectronic.)
1. Ba
2. Te
3. Cs
4. I
013 10.0 points
Which of the following has the largest radius?
1. S
2−
2. K
+
3. Cl
4. Cl
−
5. S
014 10.0 points
What is the order of decreasing ionization
energy?
1. tellurium, selenium, oxygen
2. oxygen, selenium, tellurium
3. selenium, oxygen, tellurium
4. selenium, tellurium, oxygen
5. oxygen, tellurium, selenium
6. tellurium, oxygen, selenium
015 10.0 points
Which atom is smaller?
1. Unable to determine
2. bromine
3. iodine
4. They have the same size.
016 10.0 points
Rank the following species from smallest to
largest atomic radius: K, Mg, Rb, Ca.
1. Rb < K < Ca < Mg
2. Mg < Ca < K < Rb
3. Mg < Ca < Rb < K
4. Mg < Rb < K < Ca
5. Mg < K < Ca < Rb
017 10.0 points
Francium (atomic number 87) would be expected to have a (large,small) first ionization
potential and a (large, small) electronegativity.
1. large; large
2. small; small
3. large; small
4. small; largepenwell (blp865) – HW 12 Periodic Trends – thompson– (991918292) 4
018 10.0 points
Consider the following ground-state electronic
configurations. Which atom has both the
highest first ionization energy and the highest
electron affinity?
1. [Ne] 3s
2
3p
4
2. [Ne] 3s
2
3p
5
3. [Ne] 3s
2
3p
1
4. [Ne] 3s
2
3p
3
019 10.0 points
The energy needed to remove electrons from
an atom is called
1. bonding energy.
2. ionization energy.
3. valence energy.
4. network energy.
020 10.0 points
Rank the following atoms and ions
Li
+
, Be
2+
, He, H
−
, B
3+
in order of decreasing size.
1. B
3+
, Be
2+
, Li
+
, He, H
−
2. B
3+
, Be
2+
, He, Li
+
, H
−
3. H
−
, Li
+
, He, Be
2+
, B
3+
4. He, H
−
, Li
+
, Be
2+
, B
3+
5. H
−
, He, Li
+
, Be
2+
, B
3+
021 10.0 points
Rank the following in terms of decreasing
ionic radii.
1. F
−
, O
2−
, N
3−
, Na
+
, Mg
2+
2. Na
+
, Mg
2+
, O
2−
, N
3−
, F
−
3. N
3−
, O
2−
, F
−
, Na
+
, Mg
2+
4. Mg
2+
, Na
+
, F
−
, O
2−
, N
3−
5. Na
+
, Mg
2+
, N
3−
, O
2−
, F
−
022 10.0 points
What is the order of decreasing atomic radius?
1. chromium, titanium, cobalt
2. titanium, cobalt, chromium
3. cobalt, titanium, chromium
4. titanium, chromium, cobalt
5. cobalt, chromium, titanium
6. chromium, cobalt, titanium
023 10.0 points
Atoms with loosely held valence electrons
have
1. high ionization energy and high electron
affinity.
2. low ionization energy and low electron
affinity.
3. low ionization energy and high electron
affinity.
4. high ionization energy and low electron
affinity.